1. Field of the Invention
The present invention is related to an automatic illumination intensity control apparatus for a discharge lamp such as a fluorescent lamp, and particularly to an automatic illumination intensity control apparatus for a discharge lamp for automatically maintaining the brightness of the area to be illuminated at an intensity set by the user, and preventing any overcurrent from flowing through the discharge lamp.
2. Description of the Prior Art
Recently, various improvements are have been achieved in the art of illumination intensity control which can vary the illumination intensity of a discharge lamp by an inverter-type drive circuit.
FIG. 1 is a block diagram schematically illustrating a conventional discharge lamp ballast with an illumination intensity control.
Referring to FIG. 1, the discharge lamp ballast includes a discharge lamp 22 such as a fluorescent lamp, a control knob 10 for setting a duty cycle which allows the illumination intensity control of the discharge lamp 22, an oscillator 12 for generating an oscillating signal with a predetermined frequency, a frequency convertor 14 for converting the frequency of the oscillating signal into different frequency, a variable pulse width modulator 16 for varying the on-off duty cycle of the signal output from the frequency converter 14 according to the on-off duty cycle set by the control knob 10, a switching element 18 turned on or off by the modulating signal from the variable pulse width modulator 16, and a first and second transformer 20 obtaining induced voltage according to the turning on-off of the switching element 18.
In the afore-mentioned discharge lamp ballast the intensity of illumination is controlled by varying the electrical power delivered to the discharge lamp 22 according to the on-off duty cycle set by the control knob 10. Further explanation of the prior art will be omitted in this specification because the details are disclosed in U.S. Pat. No. 4,998,046.
However, the conventional art has a problem in that an additional wire member should be undesirably provided in a wire transmission, and manufacturing cost becomes expensive in a wireless transmission, that is, a remote control.
Moreover, the output of the discharge lamp is fixed to the level set by the user without any consideration to the natural brightness of the area that is to be illuminated.
Furthermore, the frequency band used overlaps with that of a general remote control, thereby causing other electric appliances to malfunction.